Known in the art is a spark ignition type internal combustion engine comprising a variable compression ratio mechanism which is able to change an mechanical compression ratio and a variable valve timing mechanism which is able to control a closing timing of an intake valve, wherein an amount of intake air which is supplied into a combustion chamber is mainly controlled by changing the closing timing of the intake valve and wherein at the time of engine low load operation, the mechanical compression ratio is higher than at the time of engine high load operation (for example, PLT 1).
In particular, compared to the actual compression ratio, the mechanical compression ratio (that is, the expansion ratio) has a larger effect on the theoretical heat efficiency. Therefore, in the spark ignition type internal combustion engine which is described in PLT 1, during engine low load operation, the actual compression ratio is maintained low while the mechanical compression ratio is a high value of, for example, 20 or more. Due to this, in the spark ignition type internal combustion engine which is described in PLT 1, it is possible to make the theoretical heat efficiency an extremely high value. Along with this, the fuel efficiency is greatly improved.